Today's internal combustion engines must meet difficult and sometimes conflicting requirements in order to be commercially successful. It is desirable that an internal combustion engine be efficient, perform well over a varied load, have good fuel economy, require only limited maintenance and emit little or no atmospheric pollution.
One requirement is that the engine be capable of using fuels other than gasoline or diesel. The fact is that petroleum based products are not renewable. Once society has consumed the earth's supply of oil, most conventional internal combustion engines will no longer to useful. Thus, there is a need for an internal combustion engine that burns alternative fuels.
Another demand is that the engine must also have a respectable power output. Even if it possesses all the other advantages mentioned herein, an engine that cannot generate power has no real commercial value.
Yet another demand is that engines be cleaner-burning. Concern with pollution due to exhaust fumes is more prevalent today than ever before. In order to curb such pollution, many laws have recently been enacted to regulate emissions. Moreover, the environmental movement has exerted increased pressure to clean up engine exhausts. Some existing engines offer a trade-off between low emissions of nitrogen oxide (NOX) and carbon monoxide (CO) and low emissions of hydrocarbons. For example, a stratified charge engine gives low emissions of NOX and CO because a spark ignites a mixture of air and fuel in a zone rich in fuel. The stratified charge engine, however, tends to have high emissions of unburned hydrocarbons because the combustion flame is quenched by the lean air/fuel ratio before all the fuel is burned. Other engines have attempted to address this concern. One regenerative, internal combustion engine is illustrated in U.S. Pat. No. 4,781,155 entitled Regeneratively Acting Two-Stroke Internal Combustion Engine, issued on Nov. 1, 1988 to H. G. Brucker. This engine includes a combustion cylinder and a supercharger cylinder, with the possibility of re-expanding combusted gases in the supercharger cylinder. This re-expansion improves pollutant emission.
Also in order to improve efficiency and power output, a compressed air-fuel mixture may be pre-heated before ignition. Preheating helps to optimize the combustion process within an engine, but preheating at too high a temperature may cause combustion prior to the desired moment when work can be effectively done on a piston. The mixture should not prematurely ignite during the preheating process. One type of multicylinder engine that provides for preheating is illustrated in U.S. Pat. No. 4,715,326 entitled Multicylinder Catalytic Engine, issued on Dec. 29, 1987 to R. H. Thring. This engine uses a heat exchanger for heating a mixture of compressed air and fuel using heat captured from the exhaust gases. Another type of internal combustion engine that provides for preheating is illustrated in U.S. Pat. No. 5,050,570 entitled Open Cycle, Internal Combustion Stirling Engine, issued on Apr. 5, 1989 to R. H. Thring. This engine uses a regenerator for heating compressed air using heat captured from exhaust gases. Both U.S. Pat. Nos. 4,715,326 and 5,050,570 are incorporated by reference for all purposes within this application.